2000-02-16 04:00:00 PDT TAHOE -- An unprecedented study of environmental troubles in the Lake Tahoe Basin gives the fabled Sierra region as little as 10 more years of healthy life unless strong measures are taken to control water runoff and air pollution.

The 1,200-page Lake Tahoe Watershed Assessment being released today compiles 20 years of scientific data with the results of a two-year crash research program and is designed to avert what could be one of the West's worst ecological disasters -- one that also would have dire economic consequences for the tourism industry.

"We have a decade or two left to do something or we lose the water quality of Lake Tahoe forever," said study co- author Charles Goldman, emeritus professor at the University of California at Davis.

That projected life expectancy of the lake was based on current rates of phosphorous and nitrogen runoff, among other pollutants contributing to algae blooms.

Already, floating mats of algae are seen in some areas as the lake loses water clarity at the rate of about one foot a year. Unless the trend is stopped in time, scientists said, the damage will be irreversible, putting Lake Tahoe on track to become as dead and dark as Clear Lake -- one of California's more notable foul-water disasters.

Tahoe's troubling loss of water clarity was traced to a thicket of tough problems, including:

-- Water that runs off the roads each spring, carrying road salt and other fine materials into streams that empty into the lake.

-- Building activity in the Tahoe watershed, which disturbs soils and adds to the natural runoff of clay.

-- Fire suppression, which prevents natural small-scale fires from clearing brush and downed timber. That leads to more damaging catastrophic fires and unhealthy forests, adding to the lake's woes.

The study resulted from a multiagency effort begun in 1997 at the behest of President Clinton's administration after a presidential tour of the famed blue jewel of the Sierra.

It outlines a complicated mix of air, water and forest-management woes --

and sets the stage for a new era of environmental study and protection efforts.

A formal announcement was scheduled for today, when the full report will be released. Plans call for the institutions to share existing laboratories in the Tahoe region in a so-called Tahoe Environmental Science System, as well as new labs planned by the two universities. A $5 million grant is being sought from the National Science Foundation.

Tahoe's environmental champions and regulatory watchdogs said the study did not answer some of the most critical questions, however, including the exact source of the phosphorous runoff that is clouding crystalline waters made famous by Mark Twain and millions of travelers who followed in his footsteps.

Still, the study, for all its dry prose and rows of estimated effluent tonnages, represents a "great stride forward" in terms of breaking the bureaucratic infighting that has long stymied protection efforts, said Chris Knopp, natural resource staff officer at the U.S. Forest Service Tahoe Basin Management Unit.

One of the report's central findings is that environmental protection will go nowhere in Lake Tahoe unless the impact on human activities is taken into full account.

"No realistic solution will arise from the environmental perspective without paying attention to the socioeconomic consequences," Knopp said.

Tom Cahill, a UC Davis atmospheric scientist and physicist, said one of the study's take-home messages is that Lake Tahoe in prehistoric times was quite different than it is today. For one thing, the air was much smokier in the summers.

"Typically there was an average of 30 acres of the Tahoe basin burning every day from May to October," Cahill said. "And that was a good thing."

FEWER FIRES CREATE HAZARD

Now, the forests have grown weedy with small pines and too many fast-growing trees and scrub, far more than can be justified by the region's natural cycle of growth and decay.

"Tahoe has three times as many trees as can be supported," Cahill said. "We have the wrong kind of trees and too many trees."

The stately Jeffrey pines that used to dominate the area stored their nitrogen in the needles, and were protected from the periodic small fires that raged at their roots. Today, thickets of greenery create a constant threat of devastating fires that can cook streams, eradicate amphibians -- and release tons of algae-feeding nutrients into the lake.

Ozone levels in the area are getting worse despite cleaner fuels and two decades of air-pollution controls that have delivered clearer air to most other regions of the state. Scientists traced that problem to traffic tie-ups on Interstate 80 and Highway 50.

Even if all current runoff were eliminated, Knopp said, it would take another 20 to 30 years before visible benefits are seen because so much lake sediment is roiled to the surface with seasonal changes in water temperature.

And there is little chance of any immediate consensus to stop the runoff, given some striking gaps in scientific knowledge unearthed by the new study. Most notable was the study's failure to pinpoint just where the bad stuff is coming from.

Phosphorous, for example, is pouring into the lake at the estimated rate of 45.7 metric tons a year. But scientists said the source of the phosphorous that does the most damage is unclear, as is the most effective way to stop it.

Possible sources include such disparate sources as wood-burning stoves, residual discharge of old underground tanks and vehicle emissions.

There is no mystery, however, about the result. At current rates, the lake will lose about 30 feet of clarity by 2030 -- despite all the past efforts to keep Tahoe clear.

"The bottom line is we're still losing the lake," Cahill said.

HIGHLIGHTS OF TAHOE STUDY

-- Tahoe will lose about 30 feet of water clarity by 2030 at current rates. -- Lake color would change from cobalt blue to green because of estimated algae growth of 5 percent a year. -- Clear summer air in the modern era is an anomaly related to harmful suppression of small-scale summer fires, which, in past years, helped keep forests healthy and limited damaging runoff and catastrophic fires. -- Interaction of several problems -- urbanization, habitat loss, air pollution and soil erosion -- are at the root of the lake region's problems, and thus a multidisciplinary, multiagency approach is needed to fix them. -- No effective solutions are possible without economic impacts taken into account. -- Six institutions and government agencies --
University of California at Davis
, University of Nevada at Reno, Desert Research Institute, U.S. Geological Survey, Stanford University and the U.S. Forest Service -- agreed to cooperate on further research in the Tahoe Basin, including sharing new laboratories and technical services.